Quiet jet discharge nozzle

ABSTRACT

An improved air/gas jet nozzle of the multiple orifice form is disclosed, the output of which is substantially inaudible to the human ear. The nozzle comprises an airfoil-shaped plenum having &#39;&#39;&#39;&#39;paper thin&#39;&#39;&#39;&#39; slot-shaped orifices in its trailing edge. Sheaths of inaudible range vibrating air are induced to surround the flat-wise extenuating discharge streams from the nozzle orifices to mask the audible range sound vibrations therein.

United States Patent Paxhia et al.

[451 Feb. 11 1975 QUIET JET DISCHARGE NOZZLE Inventors: Vincent B. Paxhia, Tonawanda;

Franklin B. Bossler, Williamsville, both of NY.

Assignee: Textron, Inc., Providence, R.I.

Filed: July 10, 1972 Appl. No.2 270,180

US. Cl 239/568, 181/33 F Int. Cl. B05b l/14 Field of Search 239/67 A, 568, 265.19,

References Cited UNITED STATES PATENTS 8/1958 Tyler et a1. 181/33 F FOREIGN PATENTS OR APPLICATIONS 514,913 11/1939 GreatBritaln 181/60 859,272 6/1940 France ..181/60 Primary Examiner-Lloyd L. King Attorney, Agent, or FirmBean & Bean [57] ABSTRACT An improved air/gas jet nozzle of the multiple orifice form is disclosed, the output of which is substantially inaudible to the human ear. The nozzle comprises an airfoil-shaped plenum having paper thin slot-shaped orifices in its trailing edge. Sheaths of inaudible range vibrating air are induced to surround the flat-wise extenuating discharge streams from the nozzle orifices to mask the audible range sound vibrations therein.

7 Claims, 7 Drawing Figures 1 QUIET JET DISCHARGE NOZZLE BACKGROUND AND OBJECTS OF THE INVENTION Quiet and efficient discharge of air or other gases .or fluids (hereinafter referred to as air) via jet devices for thrust generation purposes has long been a soughtfor goal in various industries. Such devices improve any air discharge system operating in an environment where acoustic vibrations at audible levels are intolerable or undesirable. The present invention evolved from the invention set forth in copending Pat. application Ser. No. 152,696 filed June I4, 1971, now U.S. Pat. No. 3,695,388; and differs from the heretofore popular theory that the blending into a jet stream of relatively large amounts of ambient or secondary" air would avoid undesirably perceived noise effects. The present invention again provides a surprisingly improved advance in this technology.

As explained in the copending application hereinabove referenced, whereas previously respected theories in connection with this problem have been based upon belief that noise at undesirable levels is generated as a result of shearing action between colliding streams of relatively high and low velocity air; we have ascertained that such theories are inadequate and erroneous, and that surprisingly improved results may be attained by forcing the acoustic wavelengths of the exiting jet stream to be so small that the resulting sound may be rapidly attenuated by molecular absorption into a sound-masking envelope of relatively viscous air derived from the ambient atmosphere, until such time as it becomes attenuated and inaudible to the human ear. In order to achieve this result (while still maintaining efficiency of the nozzle for propulsion purposes) the present invention contemplates a still further improved form of multiple-orifice nozzle construction embodying novel orifice shapes and positional relationships, and jet stream velocities which are as highas possible without being supersonic; the nozzle orifices being as small as possible without producing excessive thrust losses due to jet air/gas viscosity characteristics.

THE DRAWING The invention is illustrated by way of example by the accompanying drawing wherein:

FIG. 1 is a side elevational view of one form ofa multiple orifice nozzle of the present invention;

FIG. 2 is a rear end elevational view thereof;

FIG. 3 is a fragmentary sectional view thereof, on enlarged scale, taken as suggested by line 33 of FIG. 1; illustrating operation of the invention; and

FIGS. 4-7 are rear elevational views of other forms of nozzle constructions embodying the invention.

The present invention provides a still further new approach to the science of conversion of audible wavelength jet streams into inaudible wavelengths, by initially flattening the ultra-sonic jet blast and then encasing it within a sheath of sound masking sub-sonic ambient air which travels along with the jet blast until the sound-generating wavelengths thereof have been attenuated into inaudible levels. Thus, in one form of the invention, a single flat jet blast or jet stream" would be sheathed by an envelope of ambient air flowing alongside the entire periphery of the jet stream; but only within other specific parameters as explained hereinafter. Hovever, in order to convert the concept of the present invention into practical hardware, a very large number of small flat jet orifices are required, and it is r at this point that the invention further distinguishes from the prior art.-

Whereas it has been found that multiple jets of certain configurations will produce a predicted small wavelength noise in almost any arrangement, undesirable long wavelength noise is also produced as a byproduct thereof unless the nozzle orifices are arranged so that each issuing jet is permitted to act and react with the ambient air as though it were an isolated jet. The purposes of the present invention may be attained either by providing a single oriented row of paperthin" sized orifices properly spaced apart as will be explained hereinafter, or multiple rows of properly spaced .apart orifices providing directionally divergent jet paths, as will also be explained hereinafter.

Nozzle plenums to which the present invention may be applied may be constructed in a variety of forms as shown by way of example in the accompanying drawing; and as shown therein a preferred form of the nozzle plenum may be provided to comprise a hollow shell 10 which is elongated in at least two directions so as to provide a walled chamber for supplying and accommodating a plurality of jet stream thin and slot-shaped discharge orifices 12. The shell 10 is externally airfoilshaped as illustrated at FIG. 3, and is mounted in flow communication with any preferred form of pressured fluid supply conduit such as illustrated at 14.

As shown in FIG. 3, the rear edge portion of the shell I0 is wedge or oval-shaped and terminates in a trailing edge 18. As shown at FIGS. I, 2, the orifices 12 are disposed horizontally and arranged in a single vertical row, exiting directly through the trailing edge portion 18 of the nozzle. It will be apparent from examination of FIG. 3 of the drawing herewith, that the ejector action of the air through the orifices 12 will induce flow of ambient air 20 around the shell 10 and then around each high velocity jet 22 of air so as to envelop it while it travels for a substantial distance away from the nozzle. The air flows to the orifices through specifically designed and shaped conduits 16 which receive air/gas under pressure from the plenum 14, as will be further described hereinafter.

As stated in application Ser. No. l52,696, the present invention also contemplates that each ultra-sonic jet stream issuing from an orifice induces flow therearound of an external shell of sound-masking sub-sonic ambient air; the orifices 12 being so relatively spaced that the induced air flow streams avoid interference with each other whereby noise supression is obtained. Various patterns of multiple slot arrangements were tested with this object in mind; whereupon it was discovered that when working with a plural parallel of rows of orifices greatly improved results are attainable by arranging the orifices at the trailing edge of the nozzle as shown at FIGS. 4-5 herewith. Such arrangements cant the orifice slots in slightly opposite directions laterally of the center line of the multiple orifice array. The externally streamlined shape of the nozzle shell l0 and the streamlined form of the internal conduit 16 as shown in FIG. 3 cooperate to assist the jet streams issuing from the slots 12 to fan out and attenuate. FIGS. 6, 7, show alternative multiple slot arrangementswherein the slots are disposed vertically. Here again, the slots are preferably cut through the nozzle shell 10 so as to cant dihedrally" relative to the median camber line of stream discharge orifices are cut through the trailing edge wall section of the nozzle as shown; and it has been determined that the orifice width and length dimensions should be such that air will be discharged therethrough in a flat fan pattern at a rate less than Mach l, and preferably between Mach 0.6and 0.8- or thereabove; approaching but never reaching Mach 1. Such results are attained for example byfurnishing the air/gas to slots of about 0.020 inches wide at pressures up to about l psi. The slot-shaped exits should then be relatively spaced apart within the range of 1.5 to 6.0 times the slot widths. A preferred positional arrangement for an array of exit slots as shown in FIG. 1 herewith would locate the slots on centers approximately five slot widths apart.

It will be recognized that-while every effort is made to reduce pressure losses in the slots and the associate ducting, such losses to some degree will be encountered. However, it has been found that the effect of such losses on propulsion system performance can be minimized in accordance with the present invention. In addition to the external arrangement of the nozzle orifices as shown herein, it is important that the internal forms of the feed channels to the discharge slots must be such that no excessive turbulence be created in the throat sections thereof, such as would result from the presence of sharp corners and edges interiorly of the feed channel. The flow of air/gas must completely fill the feed channels in order to generate the required thrust with minimum losses. It is also important that the plenum casing be of an external shape of aerodynamic smoothness, so that the pcrformmance of the nozzle is not adversely affected either as to noise production or thrust efficiency, as a result of motion of the ambient air relative to the nozzle assembly.

As explained in copending application Ser. No. 152,696, nozzle efficiency is defined as the ratio of the actual thrust obtained to the thrust that could be theoretically obtained by isentropic expansion for the same mass flow rate and pressure ratio. This distinction is very important. In practice, duct and nozzle losses may be largely offset by providing slightly larger nozzle areas, to restore the mass flow rate to the ideal flow. The loss of thrust is then proportional to the square root of the pressure loss instead of being directionally proportional to it.

For sound abatement purposes the sound pressure from the jet orifices should be predominately at frequencies at the upper range of audibility and beyond. in addition, the influence of nozzle-exit diameters and relative spacings apart as well as nozzle-exit velocities,

are critical. Although smaller jet orifices provide a lower overall noise level, their fabrication and operative maintenance is more difficult. Therefore, the largest sized slot-shaped orifice consistent with minimum audible frequencynoise requirements should be employed.

- Although we have shown herein certain preferred embodiments of orifice arrangements, it will be understood that other arrangements may be employed depending upon the thrust distribution requirements.

We claim:

1. An inaudible thrust producing discharge nozzle device comprising an externally airfoil-shaped plenum having a trailing edge and air discharge orifice means extending through the wall portion of said trailing edge,

said orifice means including arow of separate orifices of thin slot-like section directing discharge of high speed air jet streams from said plenum rearwardly of said trailing edge and being relatively spaced apart so as to induce flows of air from the ambient atmosphere encasing each high speed discharge jet "stream within a non-turbulent sheath of inaudible range vibrating air, thereby masking the audible range sound propogations of said jet streams until they are attenuated and reduced to inaudible levels) 2. Anozzle as set forth in claim 1 wherein said orifice means comprises two rows of slot-shaped orifices directed to exit at opposite sides of said trailing edge and at staggered spaced apart positions symmetrically thereof.

3. A nozzle as set forth in claim 2 wherein said orifices are directed to discharge from opposite sides of said trailing edge jet streams travelling in divergent directions.

4. A nozzle as set forth in claim 1 wherein the ratio of the thickness of said orifices to the rate of flow therethrough is such that the velocity of jet stream flow at the orifice exits is less than Mach 1.

5. A nozzle as set forth in claim 4 wherein the velocity of jet stream flow at the orifice exits is between 0.6 to 0.8 Mach.

6. A nozzle as set forth in claim 4 wherein the rate of jet stream flow at the orifice exits is greater than 0.5 Mach and less than Mach 1. I

7. A nozzle as set forth in claim 1 wherein said orifice means comprises orifices arranged parallel to said trailing edge, said orifices being in a single line or at staggered spaced apart positions symmetrically-thereof. 

1. An inaudible thrust producing discharge nozzle device comprising an externally airfoil-shaped plenum having a trailing edge and air discharge orifice means extending through the wall portion of said trailing edge, said orifice means including a row of separate orifices of thin slot-like section directing discharge of high speed air jet streams from said plenum rearwardly of said trailing edge and being relatively spaced apart so as to induce flows of air from the ambient atmosphere encasing each high speed discharge jet stream within a non-turbulent sheath of inaudible range vibrating air, thereby masking the audible range sound propogations of said jet streams until they are attenuated and reduced to inauDible levels.
 2. A nozzle as set forth in claim 1 wherein said orifice means comprises two rows of slot-shaped orifices directed to exit at opposite sides of said trailing edge and at staggered spaced apart positions symmetrically thereof.
 3. A nozzle as set forth in claim 2 wherein said orifices are directed to discharge from opposite sides of said trailing edge jet streams travelling in divergent directions.
 4. A nozzle as set forth in claim 1 wherein the ratio of the thickness of said orifices to the rate of flow therethrough is such that the velocity of jet stream flow at the orifice exits is less than Mach
 1. 5. A nozzle as set forth in claim 4 wherein the velocity of jet stream flow at the orifice exits is between 0.6 to 0.8 Mach.
 6. A nozzle as set forth in claim 4 wherein the rate of jet stream flow at the orifice exits is greater than 0.5 Mach and less than Mach
 1. 7. A nozzle as set forth in claim 1 wherein said orifice means comprises orifices arranged parallel to said trailing edge, said orifices being in a single line or at staggered spaced apart positions symmetrically thereof. 